694 DESCEIPTIVE GEOLOGY, 



extreme metamorphism, and where the strata are encircled and abruptly 

 cat off by the more recent volcanic rocks. As the strata assume a north 

 and south direction, the dip becomes east, varying from 28° to "40°. It 

 seems to be essentially a monoclinal ridge, and to have been broken on a 

 north and south line, and thrust up into its present position; no evidences 

 being observed along the west base of any westerly-dipping beds. There 

 is, however, at the extreme western base of Granite Mountain, in the narrow 

 strip of Quaternary between the granite and the alkali flat, a low obscure 

 outcrop of limestone, dipping west at an angle of about 30°, and striking a 

 few degrees west of north and east of south. ' This probably represents the 

 western connection of the monoclinal ridge already described. If it was a 

 fold, the east half has been lifted at least 5,000 feet, and the same is true if 

 it is a simple monoclinal block. In the valley between McKinney's Pass 

 and Buffalo Canon, West Humboldt Range, the structural problem is some- 

 what obscure, and is apparently this: whether the strata which dip down 

 under the valley from Buffalo Peak rise again and form the western half of 

 an anticlinal, of which the McKinney Pass mass is the eastern side, or 

 whether the Buffalo Peak strata flatten out under the valley, and the 

 McKinney's Pass ridge is simply broken up as a monoclinal block. The 

 probability is given to the idea of a westerly-dipping mass under the valley 

 by the outcrops spoken of, at the west base of Granite Mountain ; but in 

 that case it is necessary to suppose a violent faulting along the axis, with 

 such vertical displacement of the west half that the anticlinal lies fully 

 below the valley, for it is entirely improbable that erosion could ever account 

 for the absence of the west half of the fold. Much the same structure evi- 

 dently occurs north of Granite Mountain and east of Star Peak, and the 

 probability of an easterly-dipping set of strata, which are the prolongation 

 northward of the Buffalo Peak side of the anticlinal, is rendered tenable by 

 the actual existence on the east side of the West Humboldt Eange, in the 

 region of Indian Canon, of easterly-dipping limestones. The Archsean 

 mass of Granite Mountain appears to have played the part of a rigid cen- 

 tre, over which the folds and fractures have been developed. 



Directly south of Granite Mountain, and rising out of the deep Qua- 

 ternary recess, which here make^ into the -range on the west side toward 



